main wire ampacity

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Just curious has anyone experienced wire OVERHEATING of STOCK white/red or white wires on their 240zs with the 60AMP or larger alternator upgrades. im a little aprehensive of the upgrade do to the ampacity ability of alternator vs stock wire size which appears to be good for 40a max.I am doing l28et conversion with megasquirt and electric fuel pump as well as headlamp relay upgrade.I will not be hooking up rear window defrost which should lower amps a little.....ive read sevral great articals on internal regulator alternator upgrades but none seem to address current main wire size in the car.I really dont want to run new white and white red stripe wires under the dash to the amp meter unless absolutley necessary.ALSO what is the average amp draw with headlamps on low and blower motor on high....thanks

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When I did my alternator swap , I couldn't get the amp meter to work, but I didn't care since I'm going to swap all the gauges for autometer stuff this summer. I have had no trouble with wires burning up so far.

I can also run my HID's, A/C, Radio(4 speakers and amp) and wipers without breaking a sweat. I have carbs though so I don' know how much more draw a big fuel pump plus the MS ecu will cause.

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Install a fuse inline in that wire. I bought a big 80 amp fuse and holder from the local parts store, It was a bussman I believe. I ditched the fusible link and ran a wire straight from the + side of the starter motor into the fuse box, then from the fuse box to the white 10 gauge main wire. I have a 105 amp alternator and have had no problems with it. The only way you could really have a massive power surge through that wire is if your alternator shorts internally or some other short occurs in that main wire, your headlights, wiper motor, and brake lights, etc, don't really draw that much current. If you do have a power surge, that fuse will fail before anything bad happens, and before your white white/red wire has a chance to melt or catch fire.

That fuse box is a great anti-theft device too. Just pop that fuse out when you have to leave your car somewhere seedy and there's very little chance a thief would be able to figure it out. It will cut power to everything.

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I can also run my HID's, A/C, Radio(4 speakers and amp) and wipers without breaking a sweat. I have carbs though so I don' know how much more draw a big fuel pump plus the MS ecu will cause.

If you have MS and are running big fuel pumps it shouldn't affect the main power wire, you should have all of the fuel injection stuff on a separate circuit that is separately fused. I am running another ten gauge wire to the + post of the starter motor next to the main power wire to draw power for all of my fuel injection stuff. If you are drawing power for MS through the main power wire then I don't think you have it wired correctly, and that may cause issues with too much amperage through the main wire and also likely introduce a lot of noise to the MS.

EDIT: Disregard this post, I know now that everything will travel through the main power wire through the alternator. I stand corrected.

Edited March 28, 2011 by Cannonball89

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Install a fuse inline in that wire. I bought a big 80 amp fuse and holder from the local parts store, It was a bussman I believe. I ditched the fusible link and ran a wire straight from the + side of the starter motor into the fuse box, then from the fuse box to the white 10 gauge main wire. I have a 105 amp alternator and have had no problems with it. The only way you could really have a massive power surge through that wire is if your alternator shorts internally or some other short occurs in that main wire, your headlights, wiper motor, and brake lights, etc, don't really draw that much current. If you do have a power surge, that fuse will fail before anything bad happens, and before your white white/red wire has a chance to melt or catch fire.

That fuse box is a great anti-theft device too. Just pop that fuse out when you have to leave your car somewhere seedy and there's very little chance a thief would be able to figure it out. It will cut power to everything.

So, in theory, you could draw up to 80 amps through the harness from the starter lug back through the wiring harness, which was designed for 40 amps. You've removed all of the individual circuit safeties, like the headlights fusible link, and combined them all in to one 80 amp fuse. You haven't made anything safer, you've just made it more likely that you'll melt a wire before the big new fuse blows. If you added enough new loads on the harness, you could possibly melt some wires, especially if you have a short in a wire. The alternator will only put out the amps that the various loads combined sum up to.

How did you calculate that the 80 amp fuse would fail before anything else?

Edited March 28, 2011 by NewZed

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240z only has one fusible link which was rated at 80 amps. There is no headight fusible link on a 240z. Just one. The setup I describe is safer than stock because instead of a wire that is designed to slowly burn at 80 amps I have a fast acting sealed fuse. The headlights, brakelights, and everything else are seperately fused through the stock fusebox. Any short in those seperate circuits will blow that respective circuits fuse before it blows the 80 amp fuse I installed, which is only a fail safe as it is main circuit protection.

No offense you just need to know what your talking about before you condemn a set up that mirrors how the factory did it with the exception of more modern components.

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240z only has one fusible link which was rated at 80 amps. There is no headight fusible link on a 240z. Just one. The setup I describe is safer than stock because instead of a wire that is designed to slowly burn at 80 amps I have a fast acting sealed fuse. The headlights, brakelights, and everything else are seperately fused through the stock fusebox. Any short in those seperate circuits will blow that respective circuits fuse before it blows the 80 amp fuse I installed, which is only a fail safe as it is main circuit protection.

No offense you just need to know what your talking about before you condemn a set up that mirrors how the factory did it with the exception of more modern components.

my understanding is that the fuse should be sized for the respective wire size to prevent melting of wires insulathion i will agree a direct short on a main conductor would blow in an instant of time before any real damage could occur to the rest of the wire.I see both sides to this discussion thanks for the input guys....

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240z only has one fusible link which was rated at 80 amps. There is no headight fusible link on a 240z. Just one. The setup I describe is safer than stock because instead of a wire that is designed to slowly burn at 80 amps I have a fast acting sealed fuse. The headlights, brakelights, and everything else are seperately fused through the stock fusebox. Any short in those seperate circuits will blow that respective circuits fuse before it blows the 80 amp fuse I installed, which is only a fail safe as it is main circuit protection.

No offense you just need to know what your talking about before you condemn a set up that mirrors how the factory did it with the exception of more modern components.

Sorry about that, you are right, I don't know the 240Z. I was responding to the misdirected answer and I over-answered. philipl wants to know if his wires will overheat if he has 60 amps available instead of 40. The answer is "only if you add more loads."

Swapping a fast-blow fuse for a slow-blow link will just make the system more sensitive, but won't affect wire heating for normal conditions.